The present invention broadly relates to centrifuges and, more specifically pertains to a new and improved construction of a pusher centrifuge.
Generally speaking, the pusher centrifuge of the present invention comprises a housing, at least one at least approximately cylindrical sieve drum which is rotatable in the housing and has an inner space into which material to be centrifuged can be fed in at one end of the at least one sieve drum, and at least one co-rotating pusher ring which is constructed to perform an oscillating motion in the axial direction of the at least one sieve drum while transporting the at least partially dewatered centrifuging or solid material at the inner side of the at least one sieve drum in the direction toward a solid material outlet provided at the other end of the at least one sieve drum.
Such pusher centrifuges are known, for example, from U.S. Pat. No. 4,217,226, granted Aug. 12, 1980 and U.S. Pat. No. 4,209,405, granted June 24, 1980, and serve to continuously dewater a centrifuging material which is fed into the inner end of a centrifuging or free flow space by means of a feed pipe and successively dewatered at the inner side of the sieve or centrifuge drums. During this operation, the centrifuging material is gradually transported or conveyed in the direction toward a solid material outlet by means of the oscillating motion of one or several pusher rings, of which the innermost pusher ring is constructed as the pusher bottom or base, and simultaneously not yet dewatered material to be centrifuged is filled in close to the first pusher ring. Such a pusher centrifuge can comprise several sieve or centrifuge drums whereby always two neighboring or adjacent sieve or centrifuge drums oscillate relative to one another in the axial direction and the edge or edge portion of the respective inner sieve or centrifuge drum acts or functions as the pusher ring. In a one-stage centrifuge the pusher bottom or base, for example, can oscillate, while in a two-stage centrifuge the oscillating member can be, for example, the sieve or centrifuge drum. In a three-stage centrifuge the pusher bottom or base and the second sieve or centrifuge drum, for example, can oscillate, while in a four-stage centrifuge the oscillating members can be, for example, the first sieve or centrifuge drum and the third sieve or centrifuge drum.
With a pusher centrifuge of this known type, a continuous dewatering of a centrifuging material is possible in that the centrifuging material in the course of transport at the inner side of the sieve or centrifuge drums from the centrifuging material inlet up to the solid material outlet is gradually dewatered in the centrifugal space or area and reaches the solid material outlet in a substantially dewatered condition, while the filtrate or filtered matter or material outwardly penetrates the sieve or centrifuge drums and is there removed or drained off.
However, in these prior art pusher centrifuges, the rate of dewatering or the residual moisture of the removed or discharged solid material is still not at an optimum. An improvement could be achieved either by extending the dewatering time, with the result that the throughput of centrifuging material is reduced, or by raising the speed of the pusher centrifuge, although this measure is only limitedly possible because of abrasion occurring and for reasons of rigidity or stability, and such measure makes the solid material cake even compacter and thus even more impervious.
On the other hand, pusher centrifuges are known from, for example, West German Pat. No. 1,065,333, published Sept. 10, 1959, or French Pat. No. 1,295,577, granted May 2, 1962, wherein the pusher bottom or base is inclined or possesses inclined surfaces and rotates with different speeds in comparison with the sieve drum. The result of this design is a complicated construction and an additional gearing or gear unit is required. Furthermore, a loosening and circulation of the centrifuging material can only be achieved directly at the inlet, while the filter cake on or at the sieve drum is moved forward as a relatively compact and increasingly impervious mass.